Sense current generation apparatus and method

Abstract

A sense current generation apparatus constituted of: a main electronically controlled switch arranged to provide a current path for an input current; a sense electronically controlled switch arranged to generate a sense current; a voltage matching circuit arranged to adjust the voltage across the first and second terminals of the sense switch to equal the voltage across the first and second terminals of the main switch, within a predetermined maximum error voltage, such that the sense current is representative of the input current; and a voltage governor arranged to: receive an indication of the voltage across the first and second terminals of the main switch; and responsive to the received voltage indication, adjust the control voltage of the main switch such that the absolute value of the voltage across the terminals thereof is maintained above a predetermined voltage threshold greater than a boundary of the error range.

The invention claimed is: 
     
       1. A sense current generation apparatus comprising:
 a main electronically controlled switch comprising a first terminal, a second terminal, and a gate terminal, said main electronically controlled switch arranged to provide a current path for an input current; 
 a sense electronically controlled switch comprising a first terminal and a second terminal, said sense electronically controlled switch arranged to generate a sense current therethrough; 
 a voltage matching circuit in communication with said first terminal of said main electronically controlled switch and said first terminal of said sense electronically controlled switch, said voltage matching circuit arranged to adjust a voltage across said first and second terminals of said sense electronically controlled switch to equal a voltage across said first and second terminals of said main electronically controlled switch, within a predetermined maximum error voltage, such that said generated sense current is representative of the input current; and 
 a voltage governor arranged to:
 receive an indication of a value of the voltage across said first and second terminals of said main electronically controlled switch; and 
 responsive to said received voltage value indication, adjust a voltage on the gate terminal of said main electronically controlled switch such that the absolute value of the voltage across said first and second terminals of said main electronically controlled switch is maintained above a predetermined voltage threshold, said predetermined voltage threshold greater than said predetermined maximum error voltage, 
 
 a current governor arranged to receive an indication of a magnitude of said generated sense current and output a control signal so as to limit the input current so as not to exceed a predetermined current threshold; and 
 a combiner in communication with said voltage governor and said current governor, 
 said gate terminal voltage of said main electronically controlled switch adjusted responsive to an output of said combiner. 
 
     
     
       2. The apparatus of  claim 1 , wherein said predetermined voltage threshold is at least 10 times greater than said predetermined maximum error voltage. 
     
     
       3. The apparatus of  claim 1 , wherein said voltage matching circuit comprises an amplifier, a first input of said amplifier coupled to said first terminal of said main electronically controlled switch and a second input of said amplifier coupled to said first terminal of said sense electronically controlled switch, said predetermined maximum error voltage range responsive to an offset voltage error of said amplifier. 
     
     
       4. The apparatus of  claim 1 , wherein said combiner comprises:
 a first combiner electronically controlled switch, a control port of said first combiner electronically controlled switch in communication with an output of said voltage governor, a first terminal of said first combiner electronically controlled switch coupled to the gate terminal of the main electronically controlled switch; and 
 a second combiner electronically controlled switch, a control port of said second combiner electronically controlled switch in communication with an output of said current governor, a first terminal of said second combiner electronically controlled switch coupled to the gate terminal of the main electronically controlled switch. 
 
     
     
       5. A sense current generation apparatus comprising:
 a main electronically controlled switch comprising a first terminal, a second terminal and a gate terminal, said main electronically controlled switch arranged to provide a current path for an input current, wherein said first terminal of said main electronically controlled switch is in communication with a powered device; 
 a sense electronically controlled switch comprising a first terminal and a second terminal, said sense electronically controlled switch arranged to generate a sense current therethrough; 
 a voltage matching circuit in communication with said first terminal of said main electronically controlled switch and said first terminal of said sense electronically controlled switch, said voltage matching circuit arranged to adjust a voltage across said first and second terminals of said sense electronically controlled switch to equal a voltage across said first and second terminals of said main electronically controlled switch, within a predetermined maximum error voltage, such that said generated sense current is representative of the input current; 
 a voltage governor arranged to:
 receive an indication of a value of the voltage across said first and second terminals of said main electronically controlled switch; and 
 responsive to said received voltage value indication, adjust a voltage on said gate terminal of said main electronically controlled switch such that the absolute value of the voltage across said first and second terminals of said main electronically controlled switch is maintained above a predetermined voltage threshold, said predetermined voltage threshold greater than said predetermined maximum error voltage, 
 
 a control circuitry; and 
 a reference voltage electronically controlled switch responsive to said control circuitry, said reference voltage electronically controlled switch arranged to alternately couple an input of said voltage governor between a minimum reference voltage and a class reference voltage, 
 wherein said predetermined voltage threshold is responsive to the minimum reference voltage, and 
 wherein the voltage output of said class reference voltage is responsive to a class event voltage range. 
 
     
     
       6. A method of generating a sense current, the method comprising:
 enabling a main electronically controlled switch to provide a current path for an input current, the main electronically controlled switch comprising a first terminal, a second terminal and a gate terminal; 
 adjusting a voltage across a first and second terminal of a sense electronically controlled switch to equal a voltage across the first and second terminals of the main electronically controlled switch, within a predetermined maximum error voltage; 
 responsive to said sense electronically controlled switch voltage adjustment, generating a sense current through the sense electronically controlled switch, said generated sense current representative of the input current; 
 receiving an indication of a value of the voltage across the first and second terminals of the main electronically controlled switch; 
 responsive to said received voltage value indication, adjusting a voltage at the gate terminal of said main electronically controlled switch such that the voltage between the first terminal and the second terminal of said main electronically controlled switch is maintained above a predetermined voltage threshold, said predetermined voltage threshold greater than said predetermined maximum error voltage; 
 receiving an indication of a magnitude of said generated sense current; and 
 responsive to said received current magnitude indication, further adjusting the voltage at the gate terminal of said main electronically controlled switch so as to maintain the input current below a predetermined current threshold. 
 
     
     
       7. The method of  claim 6 , wherein said predetermined voltage threshold is at least 10 times greater than the predetermined maximum error voltage. 
     
     
       8. The method of  claim 6 , further comprising:
 coupling the first terminal of the main electronically controlled switch to a first input of an amplifier; and 
 coupling the first terminal of the sense electronically controlled switch to a second input of the amplifier, 
 wherein said predetermined maximum error voltage is responsive to an offset voltage error of the amplifier. 
 
     
     
       9. The method of  claim 6 , wherein said further adjusting comprises:
 controlling a first combiner electronically controlled switch whose output is coupled to the gate terminal of the main electronically controlled switch so that the voltage between the first terminal and the second terminal of said main electronically controlled switch is maintained above said predetermined voltage threshold; and 
 controlling a second combiner electronically controlled switch so as to maintain the input current below said predetermined current threshold. 
 
     
     
       10. A method of generating a sense current, the method comprising:
 enabling a main electronically controlled switch to provide a current path for an input current, the main electronically controlled switch comprising a first terminal, a second terminal and a gate terminal; 
 adjusting a voltage across a first and second terminal of a sense electronically controlled switch to equal a voltage across the first and second terminals of the main electronically controlled switch, within a predetermined maximum error voltage; 
 responsive to said sense electronically controlled switch voltage adjustment, generating a sense current through the sense electronically controlled switch, said generated sense current representative of the input current; 
 receiving an indication of a value of the voltage across the first and second terminals of the main electronically controlled switch; 
 responsive to said received voltage value indication, adjusting a voltage on the gate terminal of said main electronically controlled switch such that the voltage across the first and second terminals of said main electronically controlled switch is maintained above a predetermined voltage threshold, said predetermined voltage threshold greater than said predetermined maximum error voltage; and 
 alternately adjusting the gate voltage of said main electronically controlled switch such that the voltage across a load coupled to the first terminal of said main electronically controlled switch is maintained at a class event voltage.